The present invention generally relates to bicycle rear derailleurs and more particularly to a bicycle rear derailleur with a damper assembly.
As is known, a bicycle derailleur performs shifting operations by shifting the chain between a plurality of adjacent sprockets of a sprocket assembly of a bicycle. A further, also very important function of the derailleur is to ensure a sufficient chain tension. A bicycle derailleur is generally constructed in the following manner. A base member is mounted to the bicycle frame. Further, a movable member is movably connected to the base member and a chain guide assembly is movable connected to the movable member with respect to rotation about a rotational axis. The movable member is movable in the axial direction, to move the chain guide assembly between the sprockets of the sprocket assembly, so that the chain may be shifted from an initial sprocket to a target sprocket. The chain guide assembly is biased in a rotational direction by a torsion spring or the like, namely in the direction of tensioning of the bicycle chain which is guided by the chain guide assembly, to maintain the chain in a tensioned state or to restore a tensioned state after an antecedent state of insufficient chain tensioning. This rotational or pivoting direction is also referred to as “chain tensioning direction.” A rotation of the chain guide in this direction increases the tension of the chain and at the same time decreases the tension of the torsion spring acting on the chain guide assembly. Depending on the current sprocket of the sprocket assembly with which the chain is engaged at a given point, the chain guide assembly will take various rotational positions relative to the movable member with regard to the axis of rotation.
Impact on the chain and the chain guide assembly not only results from the shifting of the derailleur by shifting the chain between various sprockets of the sprocket assembly, but also from riding itself. For example, when riding on uneven surfaces, the derailleur and the chain are subjected to blows and vibrations which may act on the chain guide assembly in a rotational direction opposite to the “chain tensioning direction.” A rotation of the chain guide assembly in the direction opposite to this “chain tensioning direction” increases the tension of the tension spring acting on the chain guide assembly and directly results in a reduction of the chain tension or at least results in a greater risk of a subsequent reduction of the chain tensioning below a necessary level. Negative effects may be a drop in the chain tensioning with unwanted slackness or “dangling” of the chain. In a worst case, the chain may fall off the sprocket assembly.
To face these problems, conventional solutions are provided with a damper assembly that provides a resistance to rotational movement of the chain guide assembly in the rotational direction of the chain guide assembly opposite to “chain tensioning direction.” In this respect, the known solutions each have a one-way clutch and a friction unit, which act together in such a way that the resistance regarding the rotational movement of the chain guide assembly is affected in a rotational direction opposite to the “chain tensioning direction.”
The movable member and the chain guide assembly are rotatable relative to each other, but are frictionally coupled via the friction unit and the one-way clutch, which due to the characteristics of the one-way clutch is only effective in the rotational direction opposite to the “chain tensioning direction,” so that a dynamic friction is only present in this rotational direction to act against the rotation. In the other rotational direction corresponding to a backwards rotation of the chain guide in the sense of a tensioning of the chain, the chain guide assembly is decoupled from the movable member due to these one-way clutch characteristics, so that the tensioning of the chain by rotating the chain guide assembly encounters no resistance or at least only an irrelevant degree of resistance.
Such a rear derailleur is disclosed in US 2009/0054183 A1. The derailleur includes a damper assembly having a friction unit including a plurality of axially supported friction plates. A one-way roller clutch assembly is arranged radially outwardly of these friction plates in the same axial area, which results in the necessity of a relatively large dimension for the movable member in the radial direction. An advantage of this solution is an adjustment unit having an exposed adjustment nut for adjusting the friction engagement and thus the damping force acting as resistance. This configuration allows the rider to adjust the damping force. However, for such an adjustment a tool is required and the question arises if an average rider has the necessary knowledge to adjust the damping force correctly. Further, the exposed adjustment nut is not protected from undesired rotation which may result in undesired adjustment of the damping force.
Other rear derailleurs with damper assemblies are disclosed in US 2012/0083371 A1 and US 2012/0083872 A1. These damper assemblies also include one-way roller clutch assemblies. The rotational axis of the chain guide assembly serves as an inner clutch member of the roller clutch. The friction unit includes a leaf spring encircling an outer clutch member of the roller clutch and having two end portions radially protruding between two rotational cams or alternatively between an adjustment screw and a rotational cam, which serve for adjusting a basic friction and for controlling a momentarily acting friction via a control lever or the like, so that the cyclist—according to his wishes, for example when riding on different terrain—may select the momentarily acting friction and thus the momentarily acting damping force by the control lever which is movable between two index positions. Providing the cyclist with such a choice calls for a relatively high mechanical effort.
US 2013/0203532 A1 discloses a rear derailleur that includes a sleeve-like friction element extending circumferentially around the roller clutch assembly and having a tapered or conical outer surface. The rotational axis rotatably supporting the chain guide assembly forms the inner clutch member of the roller clutch assembly. Also, U.S. Pat. No. 4,406,643 discloses several different embodiments of a rear derailleur with a damper assembly. Generally, the damper assembly includes a one-way ratchet clutch and a friction unit having axially arranged friction surfaces. One of the embodiments includes a nut threaded into an inner thread of a tubular holder or threaded onto an external thread of a support shaft and serving as counter-bearing of the friction unit including a friction plate and a dish-shaped spring. The assembly of these prior art embodiments necessarily involves an adjustment of the damping force, since the frictional engagement depends on the actual position of the nut in the respective internal thread or on the respective external thread.